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DPChallenge Forums >> Tips, Tricks, and Q&A >> DOF blurred background: how should it be?
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04/04/2004 01:31:04 AM · #1
I just have returned from Indigo book store where I was reading some literature on photography. Regretably, most of the books sped about 50% of the volume to talk about things without knowing which I would never come out for the help from a book. But somewhere there among the obvious I found an interesting comment about light spots blurred by DOF. And the accompanying picture looked exactly as one of my experiments:

the reflected lights are way out of focus and blurred, but the blur does not seem to have any falloff from the center to the edges and the edges are really sharp! The book explained that this is due to the shapening done inside the camera and could be fixed by gaussian blur of the background in post-processing (the guy is obviously unaware of DPC :-))). So, I don't like how my camera blurs everything out-of focus.

On the other hand, people having 10D or D300 show extremely smoothly washed backgrounds as if someone has applied the Gaussian blur. I don't like this either, because it is not how I see the world which is off-focus. It is not washed! It has some granularity but no sharp edges. Something more like what I saw on the pages dicussing Leica/Panasonic cameras. I don't have any specific reference at this time, but will try to find some later. Additionally, in some review of the new Tamron lense I read that it creates 'almost Leica-like' effect on the off-focus objects.

Question (finally! :-) Is there some optical quality of the lense (only Leica?) that can reproduce natural world blurring of the eye? Is there a way to obtain something similar in the shots? Filters? Software?

Please, orient me, or I am trying to catch a black cat in the darkroom ;-))
04/04/2004 09:27:34 AM · #2
How blurred the background is depends on a few things two of which are distance from main subject and aperture of the lens being used. Both are related to depth of field.

Large apertures (smaller numbers) will produce the greatest depth of field whereas small apertures will produce shallow depth of field. In the latter case, if the background is far away it will just be a wash of colour. If the background is close then you will get some detail.

If I understand you correctly you like images with the greatest amount of DOF therefore producing only a limited blur of the background.

I appologize if I've totally missed the point/question you were presenting.
04/04/2004 10:24:41 AM · #3
The background blur is called "boke" or "bokeh" and it's one of those things that is sort of an intagible quality of certain lenses. It's a blurring effect, it's not a concrete performance item that can be measured, so people just say a lens has "nice bokeh" or not.

It comes from the shape of the apeture, and the smoother the opening, the "nicer" the bokeh. For example, the link below shows a picture taken with a 3-bladed triangular apeture, and the bokeh is wacky. The more blades on the apeture, hence a rounder opening, the nicer the bokeh.

This link is one of the better articles I've seen describing the details:

//www.luminous-landscape.com/essays/bokeh.shtml

FWIW, all of their tutorial essays are outstanding. Some of'm are pretty tech-oriented, tho.
04/04/2004 10:50:49 AM · #4
Originally posted by Dibutil:

Question (finally! :-) Is there some optical quality of the lense (only Leica?) that can reproduce natural world blurring of the eye? Is there a way to obtain something similar in the shots? Filters? Software?


Aperture shape does have an effect on the quality of bokeh, but it is certainly not the only variable. One major is how the lens is corrected for spherical aberration. The rule goes like this: if the lens is perfectly corrected, the OOF background highlights (point light sources that appear as dots, like Dibutil's posted image) will be uniformly "filled" with sharp edges (not bad, but not considered "best"). If overcorrected, the centers will be darker than the edge (appears worse than pefect correction). If, however the lens is slightly undercorrected, the brightness of the dots will start to take on a gaussian profile, brighter in middle, less so at the edge. The rule is reversed if the OOF highlights are foreground instead of background. the undercorrected conditon is considered the best situation for bokeh, but of course it will have other effects on lens performance. One effect of shperical aberration is the introduction of a "soft focus" effect. Since the aberration is most noticeable wide open, such a lens produces some very attractive portraits, with excellent bokeh and "glowing" soft skin tones when shot wide open. Canon actually makes a lens with controllable aberration (the EF 135mm f/2.8 with Soft Focus)! Some folks spend considerable time and energy looking for a "perfect bad lens".
To sum up: for good bokeh, yes, more aperture blades are better, as are blades curved to provide a more circular opening. How a lens is corrected for certain aberrations is important as well, but you may not want to give up performance in normal shooting to achieve that "perfect" bokeh. The best solution, IMO, is to apply software where required to smooth the appearance of OOF highlights.
Finally, a comment on DSLRs. Your observation regarding the very dramatically blurred backgrounds obtainable with DSLRs. Yes, they are not strict interpretations of reality, but that's not what the photographic artist is going for. A DSLR does allow you the flexibility to shoot at smaller aperture and reduce the background blur to something that approximates what your eye would see. That is the beauty of the SLR as a tool, its flexibility.
04/04/2004 03:52:44 PM · #5
Thanks everyone for the answers!

I am still trying to find that picture made with Leica lens that I am refering to. I have noticed the "internal" structure of blurred light dots - they are not entirely smooth but have some grainity which is really hard to describe but easy to see with the unfocused eye.

I agree that form the artist's prospective this effect might not be necessary but it's damn cool!
04/04/2004 04:23:41 PM · #6
Ya know, if everyone posted REALISTIC photographs, they'll almost always look like crap. To try to capture realism in photography is a futile event.

I don't know what you mean by "Natural blurring from your eyese". Your eyes always should be in focus :) The issue is that your eyes would see what the Canon lens would see with a washed out background blur, but your eyes do scan very quickly on the current scene, and so your brain would process it such that the scene appears to be very in focus, even though you can only focus at one point at a time. If you were to cut our your eye, and project light through it,the image would be similar to a lens at various aperature depending on lighting condition, butthe background is always blurred.

Do the experiment -- look at an object very closely and focus on it, you'll see that everything behind it IS BLURRED, though your brain would try to fight it and try to make them appear to be in focus.

Leica lenses are reserved for the truly snobbish kind of photographers who would rather spend $3000 on a prime lens :) Interesting when you consider that nearly all of the National Geographic photogs use either Nikon or Canon, they must not know what reality is.

Originally posted by Dibutil:

I just have returned from Indigo book store where I was reading some literature on photography. Regretably, most of the books sped about 50% of the volume to talk about things without knowing which I would never come out for the help from a book. But somewhere there among the obvious I found an interesting comment about light spots blurred by DOF. And the accompanying picture looked exactly as one of my experiments:

the reflected lights are way out of focus and blurred, but the blur does not seem to have any falloff from the center to the edges and the edges are really sharp! The book explained that this is due to the shapening done inside the camera and could be fixed by gaussian blur of the background in post-processing (the guy is obviously unaware of DPC :-))). So, I don't like how my camera blurs everything out-of focus.

On the other hand, people having 10D or D300 show extremely smoothly washed backgrounds as if someone has applied the Gaussian blur. I don't like this either, because it is not how I see the world which is off-focus. It is not washed! It has some granularity but no sharp edges. Something more like what I saw on the pages dicussing Leica/Panasonic cameras. I don't have any specific reference at this time, but will try to find some later. Additionally, in some review of the new Tamron lense I read that it creates 'almost Leica-like' effect on the off-focus objects.

Question (finally! :-) Is there some optical quality of the lense (only Leica?) that can reproduce natural world blurring of the eye? Is there a way to obtain something similar in the shots? Filters? Software?

Please, orient me, or I am trying to catch a black cat in the darkroom ;-))
04/05/2004 12:32:52 AM · #7
Actualy, Paganini, I know a great deal about the physics of the human vision as well as optics. And when I said that I am expecting some specific kind of bluring which I saw in Leica images that means that it matches my particular eyes with my own aberrations and astigmatism (and does not mean at all that I am looking at Leica lenses ;-).

This would also be a perfect arguement in the artistic dicussion: the artist wants to deliver _his_ vision and the public is to interpret and judge.

Anyways, check thiis thread in a couple of days - I believe that I will be able to find the reference image that will show the difference.

Message edited by author 2004-04-05 00:34:13.
04/05/2004 05:16:33 PM · #8
Apparently I was mislead by my memory. I found the reference images and it is not about the optics but about the way Leica Digilux stores the data. Here is the quote from photo.net:
Originally posted by Derek Stanton, July 29, 2002:


.....Other theories regarding the Auto-Pointilism filter, and observations, is that the Digilux is cramming, and posterizing smoother color areas down to very low K sizes, in order to get them through the bus to the MMC/SD card, and out of the buffer quickly. Handling these reduced information files allows the camera to feel much faster, as it is doing so much less math intensive processing, by dropping what it feels is 'non essential data.

Nice examples of the Seurat Auto Filter, from two different cameras. "Stipple/Pointilistic" posterization predominates in the out of focus areas of these images.

Image 1
Image 2

In areas of high contrast, the LC-5 / Digilux seem to do quite a capable job of recording detail, it's just that below a certain level of contrast it just drops data like mad.


You guys should admit that this looks way cool! And in some manner reminds me of my own (personal) vision of the blurred backgrouns ;-)

I read this article long time ago and remembered only the beautiful images. Later, doing research on Leica cameras I found similar "pointilization" in the samples (FILM - too!!!) and thought that this is the lens feature, rather than software.

Nice effect, though - I don't think it can be achieved without selection of the parts of the final image. What needed is to change the level of pixelization in proportion to the phase diffrernce of the neighbouring pixels, or somehow the contrast... Have anyone seen such filter? May be a custom convolution of some sort could emulate this?

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